Binimetinib in combination with nivolumab or nivolumab and ipilimumab in patients with previously treated microsatellite-stable metastatic colorectal cancer with RAS mutations in an open-label phase 1b/2 study

Background In patients with previously treated RAS-mutated microsatellite-stable (MSS) metastatic colorectal cancer (mCRC), a multicenter open-label phase 1b/2 trial was conducted to define the safety and efficacy of the MEK1/MEK2 inhibitor binimetinib in combination with the immune checkpoint inhibitor (ICI) nivolumab (anti–PD-1) or nivolumab and another ICI, ipilimumab (anti-CTLA4). Methods In phase 1b, participants were randomly assigned to Arm 1A (binimetinib 45 mg twice daily [BID] plus nivolumab 480 mg once every 4 weeks [Q4W]) or Arm 1B (binimetinib 45 mg BID plus nivolumab 480 mg Q4W and ipilimumab 1 mg/kg once every 8 weeks [Q8W]) to determine the maximum tolerable dose (MTD) and recommended phase 2 dose (RP2D) of binimetinib. The MTD/RP2D was defined as the highest dosage combination that did not cause medically unacceptable dose-limiting toxicities in more than 35% of treated participants in Cycle 1. During phase 2, participants were randomly assigned to Arm 2A (binimetinib MTD/RP2D plus nivolumab) or Arm 2B (binimetinib MTD/RP2D plus nivolumab and ipilimumab) to assess the safety and clinical activity of these combinations. Results In phase 1b, 21 participants were randomized to Arm 1A or Arm 1B; during phase 2, 54 participants were randomized to Arm 2A or Arm 2B. The binimetinib MTD/RP2D was determined to be 45 mg BID. In phase 2, no participants receiving binimetinib plus nivolumab achieved a response. Of the 27 participants receiving binimetinib, nivolumab, and ipilimumab, the overall response rate was 7.4% (90% CI: 1.3, 21.5). Out of 75 participants overall, 74 (98.7%) reported treatment-related adverse events (AEs), of whom 17 (22.7%) reported treatment-related serious AEs. Conclusions The RP2D binimetinib regimen had a safety profile similar to previous binimetinib studies or nivolumab and ipilimumab combination studies. There was a lack of clinical benefit with either drug combination. Therefore, these data do not support further development of binimetinib in combination with nivolumab or nivolumab and ipilimumab in RAS-mutated MSS mCRC. Trial registration NCT03271047 (09/01/2017). Supplementary Information The online version contains supplementary material available at 10.1186/s12885-024-12153-5.


Background
Colorectal cancer (CRC) is the third most diagnosed cancer (10% of cancer cases) and the second leading cause of cancer-related deaths (9.4% of cancer deaths) worldwide [1].Patients with early-stage CRC can usually be cured through surgical resection of the primary tumor, but patients with metastatic CRC (mCRC) have a 5-year survival rate of only 14% [2,3].CRC is a highly heterogeneous disease with different tumor phenotypes, each with specific molecular and morphological characteristics [4].Due to these specific characteristics, CRC can be divided into discrete subclasses based on integrated molecular and clinical studies.
Comprehensive sequencing and proteomic studies have helped to define molecular subclasses of CRC, including disease that is microsatellite stable (MSS) or microsatellite-instability-high (MSI-H) [4][5][6].Data has shown that MSS mCRC tumors have a distinct etiology and treatment recommendations that differ from tumors classified as MSI-H mCRC [5][6][7].In general, immune checkpoint inhibitors (ICIs) are effective for MSI-H but not for MSS mCRC tumors [8].However, approximately 96% of patients with mCRC have tumors with an ICI monotherapy-resistant MSS phenotype [7,8].Multifactorial mechanisms may contribute to the intrinsic resistance of MSS mCRC tumors to ICI therapy such as having a lower tumor mutational burden and being poorly immunogenic [9].Furthermore, MSS mCRC tumors may have an immunosuppressive environment caused by increased levels of tumor-associated macrophages and regulatory T cells compared with MSI-H mCRC tumors [10].
In MSS mCRC, RAS mutations have been linked to more aggressive tumor biology and a shorter overall survival (OS) compared with RAS wild-type MSS mCRC [11,12].RAS belongs to a family of small G proteins, including KRAS, NRAS, and HRAS, that is responsible for controlling signaling downstream of ligand-dependent receptor activation.In mCRC overall, KRAS and NRAS activating mutations are reported in 40% and 3% to 5% of cases, respectively; HRAS activating mutations have been reported in rare cases [7,13].RAS mutations represent a clinical setting where MAPK pathway inhibition may positively modulate the efficacy of ICIs in patients with MSS mCRC.Several preclinical studies suggest that MAPK signaling may influence tumor immune escape mechanisms, including downregulation of major histocompatibility complex class 1 expression and upregulation of immunosuppressive cytokines and cell surface molecules, including PD-1 expression, which can increase T-cell infiltration into tumors and enhance the antitumor activity of PD-1 inhibitors [14,15].Therefore, combining a MEK1/ MEK2 inhibitor with ICI treatment might be a way to overcome the inherent resistance of MSS mCRC to ICI.
Binimetinib (also known as MEK162 or ARRY-438162) is a potent and selective allosteric, ATPuncompetitive inhibitor of MEK1 and MEK2 [16].In most cancers, the ERK pathway, including RAS, BRAF, CRAF, and MEK1 or MEK2, is hyperactive due to deregulation of receptor tyrosine kinases.MEK1 and MEK2 are uniquely positioned within the ERK pathway, where they process inputs from multiple upstream activating kinases following RAF activation, making them attractive drug targets.Binimetinib has been investigated both as a single agent and in combination with other agents in patients with selected advanced or metastatic CRC [16,17].The first in-human trial of binimetinib identified 60 mg twice daily (BID) as the maximum tolerated dose (MTD) and 45 mg BID as the recommended phase 2 dose (RP2D) for binimetinib monotherapy in patients with BRAF-mutant CRC [16].Preliminary results indicate that binimetinib treatment in combination with ICIs has encouraging activity and acceptable tolerability in patients with MSS mCRC [18,19].
Nivolumab is an ICI monoclonal antibody (mAb) that targets the PD-1 cell surface membrane receptor.Nivolumab monotherapy and nivolumab in combination with the ICI ipilimumab, a mAb that targets CTLA4, have been approved to treat patients with MSI-H/mismatch repair-deficient (dMMR) mCRC that has progressed following treatment with fluoropyrimidine, oxaliplatin, and irinotecan [20,21].MSS mCRC tumors generally have fewer infiltrative CD8+ T-cell populations than MSI-H tumors [22], and immuno-oncological approaches with checkpoint inhibition alone may be insufficient for patients with limited tumor immune cell infiltration.The combination of MEK inhibitors with PD-1 inhibitors and CTLA-4 inhibitors has synergically promoted durable tumor regression and longevity of tumor-infiltrating CD8+ T cells to provide additional efficacy in preclinical mouse models [14,15].
Given that MAPK pathway inhibition might overcome the resistance to ICI in patients with MSS mCRC harboring an activating RAS mutation, this multicenter, open-label, phase 1b and phase 2 trial was designed to determine the MTD, RP2D, and schedule of binimetinib treatment in combination with nivolumab with or without ipilimumab.This study was also designed to assess the safety and efficacy of binimetinib administered in combination with nivolumab or nivolumab and ipilimumab in patients with previously treated MSS mCRC with a documented RAS mutation.

Study design and participants
ARRAY-162-202 (NCT03271047) is a multicenter, openlabel, phase 1b/2 study to evaluate the safety and preliminary antitumor activity of binimetinib in combination with nivolumab or nivolumab and ipilimumab in adult participants with MSS mCRC and a documented RAS mutation who have received 1 or 2 prior lines of therapy.This study included a dose-finding phase 1b period to determine the MTD and RP2D of binimetinib, followed by a randomized phase 2 period to assess the antitumor activity of the combinations (Fig. 1).Both phases also assessed the safety, efficacy, and pharmacokinetics of binimetinib administered in combination with nivolumab or nivolumab and ipilimumab.Key eligibility criteria included participants who: (1) were ≥ 18 years of age, (2) had Eastern Cooperative Oncology Group performance status of 0 or 1, (3) had mCRC categorized as MSS by immunohistochemistry or polymerase chain reactionbased local assay at any time prior to screening or by the central laboratory, (4) had RAS mutation assessed per local assay at any time prior to screening or by the central laboratory, and (5) had received ≤ 2 prior lines of systemic therapy in the metastatic setting (maintenance therapy given in the metastatic setting was not considered a separate regimen).Key exclusion criteria included: (1) prior treatment with any MEK inhibitor; (2) prior treatment with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or anti-CTLA-4 antibody, or any other antibody or drug specifically targeting T-cell costimulation or checkpoint pathways; (3) any untreated central nervous system (CNS) lesions, unless all known CNS lesions had been treated with radiotherapy or surgery and participants remained without evidence of CNS disease progression ≥ 4 weeks after treatment, and participants must have been off corticosteroid therapy for ≥ 3 weeks; and (4) participants who had an active, known or suspected autoimmune disease.

Study objectives and endpoints
The objective of the phase 1b part was to determine the MTD and RP2D of binimetinib administered in combination with nivolumab or nivolumab and ipilimumab.The MTD was defined as the highest combination drug dosage not causing medically unacceptable dose-limiting toxicities (DLTs) in > 35% of treated participants in the first cycle of treatment, based on a modified toxicity probability interval (mTPI-2) design.Four dose levels were tested using the mTPI-2 design, a model-based approach that is guided by a prespecified decision matrix that recommends escalating, reducing, or maintaining the same dose, or stopping dose escalation based on the number of patients with DLTs observed in the dose level under evaluation.DLTs were defined as adverse events (AEs) or clinically significant abnormal laboratory values assessed as unrelated to disease, disease progression, intercurrent illness, or concomitant medications that occurred within the first 28 days of treatment and resulted in the inability to tolerate 75% dose intensity ([administered dose in mg/planned dose in mg] × 100) of binimetinib.The primary endpoint of the phase 1b part was the incidence of DLTs resulting from binimetinib in combination with nivolumab or nivolumab and ipilimumab.
The objective of the phase 2 part was to assess the preliminary antitumor activity of the treatment combinations based on Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 with a primary endpoint of overall response rate (ORR) per RECIST 1.1.The secondary safety endpoints for both parts were the incidence and severity of AEs graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.03.The phase 1b secondary efficacy endpoint was ORR per RECIST 1.1.The phase 1b and phase 2 secondary efficacy endpoints were duration of response (DOR) and rate of complete response per RECIST 1.1.

Study treatment and procedures
In phase 1b, Arm 1A participants received a starting dose of binimetinib 45 mg BID plus nivolumab 480 mg once every 4 weeks (Q4W), the US Food and Drug Administration-approved doses of both agents at the time (Fig. 1A).In phase 1b, Arm 1B participants received a starting dose of binimetinib 45 mg BID plus nivolumab 480 mg Q4W and ipilimumab 1 mg/kg once every 8 weeks (Q8W) (Fig. 1A).In Arm 1A and Arm 1B, dose de-escalation was planned as needed until the MTD/ RP2D was determined.
Tumor response was evaluated locally by the investigator according to RECIST 1.1, using computed tomography scans and/or magnetic resonance imaging with intravenous contrast.Scans were performed at screening/ Safety was assessed throughout the study, and AEs were coded using Medical Dictionary for Regulatory Activities, version 21.0, terminology.Toxicity was assessed according to National Cancer Institute Common Terminology Criteria for Adverse Events 4.03.Participants continued treatment until disease progression, development of unacceptable toxicity, or withdrawal of informed consent.

Statistical analysis
The MTD/RP2D of the combination treatment was estimated based on the anticipated probability of DLTs in cycle 1 for participants in the dose-determining set, which consisted of all phase 1b participants who met specified minimum exposure criteria and had sufficient safety evaluations during cycle 1 or who discontinued earlier due to a DLT during cycle 1.Efficacy analyses included all participants who received at least one dose of study drug.The ORR was calculated within each treatment arm and with exact (Clopper-Pearson) 2-sided 90% and 95% confidence intervals (CIs).A similar analysis was provided for the rate of complete response.An estimate of the DOR was presented descriptively.For progressionfree survival (PFS) and OS, the survival function was constructed using the Kaplan-Meier (product-limit) method.The 25%, median, and 75% PFS and OS (in months) were summarized along with 95% CIs.Kaplan-Meier estimates with 95% CIs at specific time points were summarized as well.The safety set, which consists of all participants who received ≥ 1 dose of any study drug, was used for summaries of safety data, except for DLTs for which the dose-determining set was used.Descriptive statistics were used to summarize safety data.Statistical analyses were done using SAS, version 9.4.
All-causality immune-mediated AEs were reported for 22 participants (59.5%) in the Doublet Arms and 25 participants (65.8%) in the Triplet Arms.The most frequently (≥ 4 participants) reported all-causality immunemediated AEs were diarrhea, fatigue, and dermatitis acneiform in the Doublet Arms, and diarrhea, fatigue, dermatitis acneiform, rash, and pruritus in the Triplet Arms.
A total of 16 participants (21.3%) reported AEs leading to discontinuation of any study drug.All-causality AEs leading to discontinuation of binimetinib were reported for 3 participants (8.1%) in the Doublet Arms and 13 participants (34.2%) in Triplet Arms.Two participants in the Doublet Arms permanently discontinued binimetinib due to the following all-causality AEs (reported for 1 participant each): an AE of grade 4 blood bilirubin increased that was not considered treatment related and a serious AE of grade 4 myocarditis that was considered related to nivolumab.There was also a serious AE of grade 5 acute coronary syndrome that was not considered treatment related.Thirteen participants (34.2%) in the Triplet Arms permanently discontinued binimetinib due to the following all-causality AEs (reported for 1 participant each): grade 4 bacterial sepsis, grade 4 pneumonia, and grade 3 abdominal infection.None of these events were considered treatment related.
In the Doublet Arms, the median PFS, defined as the time from start of treatment to the date of the first documented disease progression or death due to any cause, was 3.0 months (95% CI: 1.6, 3.7) in Arm 1A (n = 10) and 1.8 months (95% CI: 1.7, 3.7) in Arm 2A (n = 27).In the Triplet Arms, the median PFS was 2.4 months (95% CI: 1.7, 5.6) in Arm 1B (n = 11) and 3.0 months (95% CI: 1.8, 13.8) in Arm 2B (n = 27).The median OS, defined as the duration from the start of treatment to the time of death due to any cause, was 5.

Discussion
Aside from chemotherapy, which has limited efficacy, treatment options are lacking for previously treated patients with RAS-mutated MSS mCRC.Therefore, we undertook this phase 1b/2 study to determine if the combination of binimetinib with nivolumab or nivolumab and ipilimumab could improve outcomes for these patients, as the combination of MEK inhibition with ICI therapy has shown evidence of tumor regression even where either agent alone was only modestly effective [14,[23][24][25].
In this study, the safety profile of the RP2D triplet regimen of binimetinib, nivolumab, and ipilimumab was similar to the clinically accepted and approved doublet regimen of nivolumab and ipilimumab [20,26,27], indicating that these therapies can be given together [16,25,28].Moreover, the observed AEs for binimetinib were consistent with those reported for other MEK1/2 inhibitors, which were reversible with appropriate supportive medical care or dose modifications [16,25,28].However, based on the ORR results, adding binimetinib in combination with nivolumab in Arm 1A or Arm 2A (Doublet Arms) did not result in an additional clinical benefit.This was also the case when binimetinib was added to nivolumab and ipilimumab in Arm 1B or Arm 2B (Triplet Arms).
Even though this study was able to examine several combinations at once, data interpretation was limited due to the small number of participants in each arm of the phase 1B and phase 2 parts.Furthermore, while no tissue samples were collected to look at possible modes of action, it could be that the extent and duration of MAPK pathway inhibition was insufficient to alter the immune environment or that the preclinical data on which this study design was based was not as relevant in the real world in this patient population.Prior studies have highlighted the challenges associated with treating patients with MSS mCRC with ICI therapy [28][29][30][31].The combination of MEK inhibition and ICI therapy might not be sufficient to overcome the "immune cold" nature of the tumor microenvironment associated with MSS mCRC [32,33].In addition, alternative mechanisms that bypass the inhibition of the MAPK pathway by a MEK inhibitor in MSS mCRC could contribute to the lack of additional clinical benefit from adding binimetinib to ICI therapy [34].Despite the lack of efficacy results in this study, MEK inhibitors still have promise in MSS mCRC and are currently being tested with broader inhibitors upstream of MEK1/2 in the RAS-regulated RAF-MEK1/2-ERK pathway, including drugs targeting SHP2 and SOS [35,36].MEK inhibitors are also being tested with cell cycle inhibitors, such as drugs targeting CDK4/6, to determine their safety and effectiveness [37].

Conclusions
As there are currently approved therapies available for patients with previously treated MSS mCRC with RAS mutation that have demonstrated a survival benefit [38,39], the lack of clinical benefit with the doublet and triplet regimens in the current study does not justify further clinical development in patients with CRC.However, other ongoing MEK inhibitor combination studies may have promise for patients with RAS-mutated MSS CRC.

Table 1
Participant demographics and baseline characteristicsECOG PS Eastern Cooperative Oncology Group performance status, max maximum, min minimum

Table 2
Treatment-related adverse events experienced by ≥ 15% of participants in ≥ 1 arm by preferred term (safety set, phase 1b/2)

Table 3
Summary of best overall response per RECIST 1.1 criteria (full analysis set, phase 1b/2) CR Complete response, PD Progressive disease, PR Partial response, SD Stable disease a Best overall response is based on investigator's assessment using Response Evaluation Criteria in Solid Tumors version 1.1.
b Confirmed